Patent GB-1020487-A (GB)
Title: Improvements in or relating to electrical switching systems
Inventor: DALY CHARLES TREVOR
IPC: H04L12/54
Filed: 1962-08-30
Abstract: 1,020,487. Data storage. STANDARD TELEPHONES & CABLES Ltd. Aug. 23, 1963 [Aug. 30, 1962], No. 33277/62. Heading G4C. [Also in Division H4] An overflow storage system for use in conjunction with telegraph exchange switching equipment comprises a large capacity store having a long access time and auxiliary buffer stores for buffering data between the exchange equipment and the large capacity store. The system described is for use with the magnetic drum exchange equipment disclosed in Specification 791,216 and comprises a plurality of large capacity magnetic tape stores 30 and auxiliary ferrite core buffer stores 1, 10 serving as respective input and output buffers for the tapes 30. Transfer from exchange to overflow store.- If it is desired to initiate overflow storage for a particular route, a key corresponding to that route is operated manually to one of three positions depending on the priority of the messages required to be transmitted to overflow storage. Assuming that the tape store for the route is available, that is, is not faulty and is not in the process of being read, a signal is sent from an indicator circuit 40 to the booking search circuit in the exchange equipment and the overflow store takes its place in the queue of outgoing lines. When the overflow store receives attention, the route and priority information of a message is transmitted over a line 41, Fig. 1, to be stored in a circulatory delay line register 2, together with an overflow number for the message and a character supplied by a tape allotter circuit 3 over a lead 42 indicating the tape on which the message is to be recorded. The overflow store emits a signal over a lead 45 to the switching centre causing the cancellation of the overflow booking mark and the print out by the switching centre of the overflow number and message incoming number of the message. The tape allotter circuit 3 sets transistor switches 4 and 5 to select the drive circuit and data input of the selected tape. The data from the switching centre passes serially via a lead 43, to a 1024-bit buffer core store whence it is transferred to a register 7 for translation to 5-bit parallel form, and calculation of a parity bit. The process of filling the store 1 continues until the complete message has been transferred. While the tape is being used for recording it is scanned by a bad patch detector circuit 60 and if a bad patch is detected, the contents of the buffer store 1 is re-recorded on the tape. A counter 35 is arranged to keep an indication of the number of messages on each of the tapes. A visual indication of which routes and priorities are being sent to the overflow store can be given by means of lamps 36. Return of messages from overflow store to exchange.-An operator manually depresses a key for the route for which overflow messages are to be returned to the switching centre thereby connecting a buffer core store 10, Fig. 3, to the selected tape, stopping the transfer of further messages to the tape, and causing a control mark to be added at the end of the last message on the tape. The route and priority part of a message read from the tape is compared at 49 with corresponding data indicating which routes and priorities are ready to be returned to the drum. If the message cannot be returned to the drum, it is read back to the tape with a switch 14 in the position shown in Fig. 3. If the message can be returned to the drum, the switch 14 is changed over to effect the return. A counter (not shown) is provided to count the number of messages returned from overflow to the drum store and which have not been transmitted from the drumstore to an outgoing line. If this number reaches three, further messages are read back to the tape via switch 14. The tape reading operation continues until the whole tape has been read. If desired, all messages below a certain priority can be automatically returned to the tape via the switch 14 in a first scanning, the lower priority messages being returned to the drum in subsequent scannings.